The transparent conductive layer has been widely used, for example, in a liquid crystal displaying element, an organic EL element, a solar battery, a touch panel, an electromagnetic radiation shielding material, and an infrared ray reflection film. Examples of the transparent conductive layer include a layer of metal such as Pt, Au, Ag or Cu, a layer of an oxide or a complex oxide doped with a dopant such as SnO2, In2O3, CdO, ZnO, SnO2:Sb, SnO2:F, ZnO:Al, or In2O3:Sn, and a layer of a nonoxide such as chalcogenide, LaBe, TiN, or TiC. Of these, a layer of a tin doped indium oxide (hereinafter referred to also as ITO) has been widely used in its excellent electric properties or its ease of processability such as etching. These layers are formed according to a vacuum evaporation method, a sputtering method, an ion plating method, a vacuum plasma CVD method, a spray pyrolysis method, a thermal CVD method or a sol-gel method.
In recent years, a flat panel display employing a liquid crystal device or an organic EL element with a large area and high precision has been developed, and a transparent conductive layer with high performance is required. In order to obtain an element or apparatus with quick response to electric field in the liquid crystal device, a transparent conductive layer with high mobility of electrons is required. Since an electric current driving method is applied in the organic EL element, a transparent conductive layer with lower resistivity is required.
A vacuum deposition method or sputtering method of the transparent conductive layer forming methods provides a transparent conductive layer with lower resistivity. Industrially, a DC magnetron sputtering apparatus provides an ITO layer with high conductivity having a resistivity of approximately 10−4 Ω·cm order.
However, these physical vapor deposition methods (PVD method) form a layer by depositing a predetermined material on a substrate in a vapor phase, and require a vacuum chamber. Accordingly, an apparatus employing the methods is large, expensive, and poor in efficiency in use of materials, resulting in low productivity. Further, it is difficult to manufacture a large sized layer employing the apparatus. Since it is necessary to heat a substrate at 200 to 300° C. in order to form on the substrate a transparent conductive layer with low resistivity, it is difficult to form a transparent conductive layer with low resistivity on a plastic substrate as the substrate.
In the sol-gel method (coating method), many procedures such as preparation of a dispersion solution, coating and drying are necessary to form a layer. Further, adhesion of the formed layer to a substrate is low, and a binder resin is necessary, which lowers transparency of the product. Further, electric properties of the resulting transparent conductive layer are poor as compared with those of the layer obtained by a PVD method.
The thermal CVD method is a method in which a precursor of a coated substance is coated on a substrate according to a spin coat method, a dip coat method, or a printing method, and baked (thermally decomposed) to form a layer. This method has advantages in that a device used is simple, productivity is excellent, and a layer of a large area can be easily formed, but has problem in that a substrate used is limited, since it requires baking treatment at a high temperature of from 400 to 500° C. It is difficult to form a layer particularly on a plastic film substrate.
As a method for overcoming the demerits in that the sol-gel method (coating method) is difficult to provide a layer with high function or use of the vacuum chamber results in lowering of productivity, a method is proposed which comprises subjecting a reactive gas to discharge treatment at atmospheric pressure or approximately atmospheric pressure, exciting the reactive gas to a plasma state and forming a layer on a substrate (hereinafter referred to also as an atmospheric pressure plasma CVD method). Japanese Patent O.P.I. Publication No. 2000-303175 discloses technique which forms a transparent conductive layer employing the atmospheric pressure plasma CVD method. However, the formed transparent conductive layer has a high resistivity, approximately 10−2 Ω·cm, which is insufficient as a transparent conductive layer for a flat panel display of a liquid crystal device, an organic EL element, a PDP or an electronic paper, the transparent conductive layer being required to have a resistivity of not more than 10−3 Ω·cm. Further, the CVD method employs, as a material, triethylindium, which may ignite and explode at ordinary temperature in ambient air, and therefore, has a question of safety.